/**
 * Favicon 代理 API
 * 通过 Google、DuckDuckGo、直连 /favicon.ico 与解析页面 <link rel="icon"> 多路竞速获取 favicon（支持 ico/png/jpg/webp）
 * 注：Bing 无公开 favicon API，故使用 DuckDuckGo 作为第二源
 */

function parseDomain(input) {
  if (!input || typeof input !== 'string') return null
  const trimmed = input.trim()
  if (!trimmed) return null
  try {
    let url = trimmed
    if (!/^https?:\/\//i.test(trimmed)) url = `https://${trimmed}`
    const u = new URL(url)
    return u.hostname
  } catch {
    return null
  }
}

/** 从 HTML 中解析 <link rel="icon"> 的 href，支持 png/jpg/webp/svg 等 */
function parseFaviconFromHtml(html, baseUrl) {
  const linkRegex = /<link[^>]+>/gi
  const links = html.match(linkRegex) || []
  for (const tag of links) {
    const relMatch = tag.match(/\brel\s*=\s*["']([^"']+)["']/i)
    if (!relMatch) continue
    const rel = relMatch[1].toLowerCase()
    if (!rel.includes('icon')) continue
    const hrefMatch = tag.match(/\bhref\s*=\s*["']([^"']+)["']/i)
    if (!hrefMatch) continue
    const href = hrefMatch[1].trim()
    if (!href || href.startsWith('data:')) continue
    try {
      return new URL(href, baseUrl).href
    } catch {
      continue
    }
  }
  return null
}

function firstSuccess(promises) {
  return new Promise((resolve, reject) => {
    let rejectedCount = 0
    const total = promises.length
    const onFulfill = (value) => {
      if (!resolve.done) {
        resolve.done = true
        resolve(value)
      }
    }
    const onReject = () => {
      if (++rejectedCount === total && !resolve.done) reject(new Error('All sources failed'))
    }
    promises.forEach((p) => p.then(onFulfill, onReject))
  })
}

export async function onRequestGet(context) {
  const { request } = context
  const url = new URL(request.url)
  const domainParam = url.searchParams.get('domain') ?? url.searchParams.get('url') ?? url.searchParams.get('u')

  const domain = parseDomain(domainParam)
  if (!domain) {
    return new Response(
      JSON.stringify({
        error: 'missing_domain',
        message: '请提供 domain、url 或 u 参数，例如: ?url=https://twitter.com 或 ?domain=github.com',
      }),
      {
        status: 400,
        headers: {
          'Content-Type': 'application/json; charset=utf-8',
          'Access-Control-Allow-Origin': '*',
        },
      }
    )
  }

  const size = Math.min(256, Math.max(16, parseInt(url.searchParams.get('size') || '128', 10) || 128))

  const fetchOpts = {
    headers: {
      'User-Agent': 'Mozilla/5.0 (compatible; FaviconProxy/1.0)',
    },
  }

  // 多路：Google、DuckDuckGo、直连 /favicon.ico、解析页面 <link rel="icon">（支持 png/jpg/webp）
  const googleUrl = `https://www.google.com/s2/favicons?domain=${encodeURIComponent(domain)}&sz=${size}`
  const ddgUrl = `https://icons.duckduckgo.com/ip3/${encodeURIComponent(domain)}.ico`
  const directUrl = `https://${domain}/favicon.ico`

  // 四路竞速：任一路成功即返回，都不参与 fallback
  const googlePromise = fetch(googleUrl, fetchOpts).then((r) =>
    r.ok ? r : Promise.reject(new Error('Google non-OK'))
  )
  const ddgPromise = fetch(ddgUrl, fetchOpts).then((r) =>
    r.ok ? r : Promise.reject(new Error('DDG non-OK'))
  )
  const directPromise = fetch(directUrl, fetchOpts).then((r) =>
    r.ok ? r : Promise.reject(new Error('Direct non-OK'))
  )

  // 抓取首页 HTML，解析 <link rel="icon" href="...">，支持 png/jpg/webp/svg 等
  const fromHtmlPromise = (async () => {
    const pageRes = await fetch(`https://${domain}/`, { ...fetchOpts, redirect: 'follow' })
    if (!pageRes.ok) throw new Error('Page non-OK')
    const html = await pageRes.text()
    const baseUrl = pageRes.url || `https://${domain}/`
    const iconUrl = parseFaviconFromHtml(html, baseUrl)
    if (!iconUrl) throw new Error('No icon in HTML')
    const iconRes = await fetch(iconUrl, fetchOpts)
    if (!iconRes.ok) throw new Error('Icon fetch non-OK')
    return iconRes
  })()

  // 仅当以上四路全部失败时，才尝试 public/favicon.ico（最后才用，不参与竞速）
  try {
    const response = await firstSuccess([googlePromise, ddgPromise, directPromise, fromHtmlPromise])
    const contentType = response.headers.get('Content-Type') || 'image/x-icon'
    const body = await response.arrayBuffer()

    return new Response(body, {
      status: 200,
      headers: {
        'Content-Type': contentType,
        'Cache-Control': 'public, max-age=86400',
        'Access-Control-Allow-Origin': '*',
        'X-Favicon-Domain': domain,
      },
    })
  } catch (e) {
    // 仅当四路（Google、DDG、直连 ico、页面解析）全部失败后，才用 public/favicon.ico
    const fallbackUrl = `${url.origin}/public/favicon.ico`
    const fallbackRes = await fetch(fallbackUrl, fetchOpts)
    if (fallbackRes.ok) {
      const contentType = fallbackRes.headers.get('Content-Type') || 'image/x-icon'
      const body = await fallbackRes.arrayBuffer()
      return new Response(body, {
        status: 200,
        headers: {
          'Content-Type': contentType,
          'Cache-Control': 'public, max-age=86400',
          'Access-Control-Allow-Origin': '*',
          'X-Favicon-Domain': domain,
          'X-Favicon-Fallback': 'true',
        },
      })
    }
    return new Response(
      JSON.stringify({
        error: 'fetch_failed',
        message: '无法从多路源获取该域名的 favicon，且未找到 public/favicon.ico 作为回退',
        domain,
      }),
      {
        status: 502,
        headers: {
          'Content-Type': 'application/json; charset=utf-8',
          'Access-Control-Allow-Origin': '*',
        },
      }
    )
  }
}